Transport of perpendicular edge momentum by drift-interchange turbulence and blobs

Abstract

Turbulence in the vicinity of the last closed surface transports plasma momentum away from the core region toward the wall, and hence provides a momentum “source” that can induce net core plasma rotation as well as sheared flows in the edge. Here, numerical simulations of this process for the binormal (approximately poloidal) component of momentum are described that use a minimal two-dimensional model, in the plane perpendicular to the magnetic field, incorporating directionality (drift-waves), radial transport (Reynolds stress and blobs), and dissipation (sheath loss terms). A zonally averaged momentum conservation law is used to advance the zonal flows. The net momentum transferred to the core is shown to be influenced by a number of physical effects: dissipation, the competition between momentum transport by Reynolds stress and passive convection by particles, intermittency (the role of blobs carrying momentum), and velocity shear regulation of turbulence. It is shown that the edge momentum source adjusts to match the rate of momentum transfer into the core, keeping the edge velocity shear nearly constant. The simulation results are also compared with the predictions of quasilinear theory.